Name: Nikita Belyaev (email_not_shown)
Date: 07/25/15-06:39:48 PM Z

We've faced with a problem that we couldn't solve. It is related to imaginary parts of the traces. We have some of them to calculate and a lot of them were already calculated correctly but for one specific term we cannot get the result without imaginary part.
We've spent a lot of time using a FeynCalcFormLink procedure and also trying to apply the Scouten identity as you told us some time ago but we did not succeed because as I understand there is no common algorithm to check such kind of equivalence in the general case.

Could you probably help us to check that the trace included contains no imaginary part?

Here is the code of our calculation:
Clear["Global`*"];
<<HighEnergyPhysics`FeynCalc`
\$LeviCivitaSign = -1;

ScalarProduct[p,p]=m^2;
ScalarProduct[p1,p1]=m^2;
ScalarProduct[p2,p2]=m^2;
ScalarProduct[k1,k1]=0;
ScalarProduct[k2,k2]=0;
ScalarProduct[q,q] = u^2;
ScalarProduct[q,s] =0;

Line13:= (GS[p2]-m).GA[\[Beta]1].(GS[p1]+m).GA[\[Beta]].(GS[p]-m).GA[\[Alpha]1].GS[k2].GA[\[Alpha]].(1-GA[5]);
Line14:= GS[k1].GA[\[Alpha]1].(GS[q]-GS[p1]-GS[p2]-u).GA[\[Beta]1].(GS[q]-u).(1+GA[5].GS[s]).GA[\[Beta]].(GS[q]-GS[p1]-GS[p]-u).GA[\[Alpha]].(1-GA[5]);
Line15:= (GS[p]-m).GA[\[Beta]1].(GS[p1]+m).GA[\[Beta]].(GS[p2]-m).GA[\[Alpha]1].GS[k2].GA[\[Alpha]].(1-GA[5]);
Line16:= GS[k1].GA[\[Alpha]1].(GS[q]-GS[p1]-GS[p]-u).GA[\[Beta]1].(GS[q]-u).(1+GA[5].GS[s]).GA[\[Beta]].(GS[q]-GS[p1]-GS[p2]-u).GA[\[Alpha]].(1-GA[5]);

Tr13= DiracTrace[Line13];
Tr14= DiracTrace[Line14];
Tr15= DiracTrace[Line15];
Tr16= DiracTrace[Line16];